Docker is a docking application (WindowMaker dock app) which acts as a system tray for KDE and GNOME2. It can be used to replace the panel in either environment, allowing you to have a system tray without running the KDE/GNOME panel or environment. Docker is written and designed to work with Openbox 2, but it should work fine in any window manager that supports WindowMaker dock apps. If you running WindowMaker or otherwise and experiencing problems, you should try using the -wmaker option to make docker keep a fixed size.